Update {virtual,override,final} to follow C++11 style in ash.

ash/system/chromeos/power/power_event_observer_unittest.cc

Index: ash/system/chromeos/power/power_event_observer_unittest.cc
diff --git a/ash/system/chromeos/power/power_event_observer_unittest.cc b/ash/system/chromeos/power/power_event_observer_unittest.cc
index a0d7d035f75b3c16e656d6f3c41ab856ab7fa1a4..aaaf2c7c46a0afd0cba9cee8b3cac519ca138906 100644
--- a/ash/system/chromeos/power/power_event_observer_unittest.cc
+++ b/ash/system/chromeos/power/power_event_observer_unittest.cc
@@ -15,15 +15,15 @@ namespace ash {
 class PowerEventObserverTest : public test::AshTestBase {
  public:
   PowerEventObserverTest() {}
-  virtual ~PowerEventObserverTest() {}
+  ~PowerEventObserverTest() override {}
 
   // test::AshTestBase::SetUp() overrides:
-  virtual void SetUp() override {
+  void SetUp() override {
     test::AshTestBase::SetUp();
     observer_.reset(new PowerEventObserver());
   }
 
-  virtual void TearDown() override {
+  void TearDown() override {
     observer_.reset();
     test::AshTestBase::TearDown();
   }